package com.jd.jobkeeper.server.service;

import java.util.HashSet;
import java.util.Set;

public class SnowFlake implements IdGenerator {

    /**
     * 起始的时间戳
     */
    private final static long START_STAMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 10; //序列号占用的位数
    private final static long MACHINE_BIT = 8;   //机器标识占用的位数
    private final static long DATA_CENTER_BIT = 4;//数据中心占用的位数

    /**
     * 每一部分的最大值 -1 binary is (1111...1111)
     */
    private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;


    private long dataCenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L;
    private long lastTimestamp = -1L;


    public SnowFlake(long dataCenterId, long machineId) {
        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
            throw new IllegalArgumentException("dataCenterId can't be greater than " + MAX_DATA_CENTER_NUM
                    + " or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than " + MAX_MACHINE_NUM +
                    " or less than 0");
        }
        this.dataCenterId = dataCenterId;
        this.machineId = machineId;
    }

    /**
     * Generate next id
     */
    public synchronized long nextId() {
        long timestamp = clockTime();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (timestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                timestamp = nextClockTime();
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;

        return (timestamp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
                | dataCenterId << DATA_CENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT           //机器标识部分
                | sequence;
    }

    private long nextClockTime() {
        long timestamp = clockTime();
        while (timestamp <= lastTimestamp) {
            timestamp = clockTime();
        }
        return timestamp;
    }

    protected long clockTime() {
        return System.currentTimeMillis();
    }


    public static void main(String[] args) {

        Set<Long> set = new HashSet(1000000);
        SnowFlake snowFlake = new SnowFlake(2, 3);

        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            set.add(snowFlake.nextId());
        }

        System.out.println(System.currentTimeMillis() - start);
        System.out.println(set.size());

    }
}
